Hearing devices are wearable hearing apparatuses which are used to assist the hard-of-hearing. In order to accommodate numerous individual requirements, various types of hearing devices are available such as behind-the-ear (BTE) hearing devices, hearing devices with an external receiver (RIC: receiver in the canal) and in-the-ear (ITE) hearing devices, for example also concha hearing devices or completely-in-the-canal (ITE, CIC) hearing devices. The hearing devices listed as examples are worn on the outer ear or in the auditory canal. Bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The damaged hearing is thus stimulated either mechanically or electrically.
The key components of hearing devices are principally an input converter, an amplifier and an output converter. The input converter is normally a receiving transducer e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output converter is most frequently realized as an electroacoustic converter e.g. a miniature loudspeaker, or as an electromechanical converter e.g. a bone conduction hearing aid. The amplifier is usually integrated into a signal processing unit. This basic configuration is illustrated in FIG. 1 using the example of a behind-the-ear hearing device. One or a plurality of microphones 2 for recording ambient sound are built into a hearing device housing 1 to be worn behind the ear. A signal processing unit 3 which is also integrated into the hearing device housing 1 processes and amplifies the microphone signals. The output signal for the signal processing unit 3 is transmitted to a loudspeaker or receiver 4, which outputs an acoustic signal. Sound is transmitted through a sound tube, which is affixed in the auditory canal by means of an otoplastic, to the device wearer's eardrum. Power for the hearing device and in particular for the signal processing unit 3 is supplied by means of a battery 5 which is also integrated in the hearing device housing 1.
As described above, in the case of BTE-RIC hearing devices the loudspeaker is removed from the housing, which is worn behind the ear, and is located directly in the auditory canal when worn. The loudspeaker, which is also referred to as the receiver, is connected to the housing and/or the hearing device via electrical cables. It is possible to connect loudspeakers of different powers to the hearing device in order to compensate for differing severities of hearing loss.
Signals are generally transmitted to the loudspeaker via two electrical cables. A resistance in the hearing device can be measured by means of a third cable. The resistance value indicates the type of loudspeaker and provides corresponding identification information. For adjustment of the hearing device it is necessary to know the type of loudspeaker used and thus to call up the corresponding identification information via the third cable. Therefore in total a three-wire connection to the loudspeaker is required: two cables for the signal and one cable for detecting the type of loudspeaker.